I find that typically "children must play." There are those upper-level, high-profile, strongly-connected, politically-minded (that's enough adjectives) "business people" who took a database theory class while getting their degree and are suddenly experts. They just have to get their hands into SQL and write queries, no matter how inefficient, now matter how misdirected, no matter how poor they are at answering the question. They have enough pull in the company to get access to SQL and then they run a query right before going to a meeting that brings the entire production server to its knees. Telling them not to do it works for a while. Complaining to a higher up might get them a slap on the hand, but the sting goes away with time, and they are back at it again. Unfortunately there is a trade-off between writing all their queries and having no time to do anything else or just letting them play on their own.

Yes, you can deny them access, but their political pull and "absolute necessity for having access" will get them in unless you want your budget slashed for the next year. You can limit what they can do, but then they'll complain that you're "handcuffing their ability to do their job with the utmost efficiency." It's far better to build them their own sandbox to play in rather than letting them mess up the sand in everyone else's.

Of course, this reflects just a hypothetical scenario and in no way resembles any of the companies I've worked for or any of the "business people" I've worked with.